Partial renovation of the Gigerwald dam: main works successfully completed

03.04.2025 – On schedule, on time and without any major incidents: Axpo and Kraftwerke Sarganserland AG (KSL) have successfully completed the main works for the partial renovation of the Gigerwald dam (SG). The reservoir is currently being refilled, and the power plant in Mapragg is scheduled to resume operations at the end of April 2025. At the same time, work is underway to dismantle the installations. The dam crest is expected to be reopened to tourists at the end of May.

With the completion of the partial renovation, Axpo and KSL have ensured the long-term operational safety of the Gigerwald dam. The trigger for the extensive renovation work was the progressive silting up of the reservoir. The inlet structures for the bottom outlet* and the works water tunnel** were therefore moved about 20 meters upwards. Axpo and KSL are investing around CHF 25 million in this project, thereby reaffirming their commitment to renewable energies and security of supply in Switzerland. The bulk of the work was completed ahead of schedule at the end of March.

50 employees in two-shift operation

Axpo and KSL began on-site preparations as early as June 2024. In September, the reservoir was completely drained to expose the intake structure at the base of the dam. The actual construction work took place during the winter because less water flows during this period, which would have to be diverted around the construction site, and because production losses would have been greater in summer. Up to 50 employees were on site six days a week, working in two shifts. ‘Thanks to the good preparation and the great commitment of everyone involved, we were able to complete the work on schedule, according to plan and without any major incidents,’ says Axpo project manager Erich Schmid, looking back on the intensive months.

Restart of the Mapragg power plant at the end of April

The Gigerwald reservoir has been refilling since the end of March. The duration of the refilling process depends on the volume of water flowing into the reservoir and is expected to take around three weeks before the level required for the Mapragg power plant to resume operations is reached. At the same time, all construction site installations are being dismantled and the original state restored. For this reason, the path along the top of the dam wall must remain closed until the end of May.

*Bottom outlet:

The bottom outlet is the lowest, lockable opening of a dam. It is used, for example, to completely empty a reservoir. A functioning bottom outlet is of central importance for the safe operation of the dam. If silting progresses to the level of the bottom outlet, the operator must take measures.

**Works Water:

The water that flows through the turbine of a hydroelectric power plant and drives it.

You can find more information on the partial renovation of the Gigerwald dam here.